Trump was aware before Wednesday's report that Tillerson had referred to him as a "moron" at the Pentagon this summer, a source familiar with the conversation told CNN, but it's unclear whether Trump discussed the remark with Tillerson. Trump was not present at the Pentagon meeting. A White House source also confirmed to CNN that Trump knew about the insult prior to Wednesday.

During a hastily arranged statement Wednesday morning, Tillerson insisted he enjoys a close relationship with Trump and called him "smart." But he would not directly deny that he'd called Trump a "moron."

"I'm not going to deal with petty stuff like that," Tillerson said from the State Department Treaty Room. "I'm just not going to be part of this effort to divide this administration."

Though Tillerson didn't deny calling Trump a moron, Trump tweeted: "The @NBCNews story has just been totally refuted by Sec. Tillerson and @VP Pence. It is #FakeNews. They should issue an apology to AMERICA!"

I told Rex Tillerson, our wonderful Secretary of State, that he is wasting his time trying to negotiate with Little Rocket Man...

Trump was flying aboard Air Force One at the time to greet survivors of Sunday's mass shooting in Las Vegas.

Trump later told reporters inside a Las Vegas hospital he has "total confidence" in Tillerson and called reports that the secretary of state called him a moron "fake news" and "totally made up."

Trump answered the question after praising the work of doctors and nurses who responded to Sunday's mass shooting on the Las Vegas strip.

Not pleased

After Tillerson's comments, a person familiar with Trump's thinking said the President is not pleased that Tillerson's terming him a "moron" has been made public, but isn't on the verge of asking for his resignation. On Thursday morning, the President tweeted that Tillerson never threatened to resign.

The President and Tillerson have an uneasy relationship, the person said, but Trump is wary of another high-profile departure from his administration after a tumultuous eight months in office.

Trump is cognizant that his administration and inner West Wing operation are shedding staff at an alarming clip. Trump has either dismissed or seen quit a chief of staff, national security adviser, press secretary, two communications directors, chief strategist, acting attorney general, FBI director, and -- as of Friday -- a Health and Human Services secretary.

Trump, above all, wants to project a sense of competence and believes the rapid turnover of staff helps fuel the notion his administration is in chaos, according to the source.

Over the past several months, Trump has been agitated -- but not outright furious -- at the distance Tillerson has put between himself and the White House on issues like Qatar, Charlottesville and North Korea.

Tillerson's pressure on Trump to certify Iran's compliance with the deal in July made him more upset, but nearly every national security official within the administration was on Tillerson's side, making it harder for Trump to fully blame his top diplomat.

Separately, another official suggested Tillerson will want to help Trump get through his November slog through Asia, an exhausting five-country tour that includes a high-stakes visit to Beijing. Tillerson was in Beijing last week to lay some of the groundwork for those talks.

Sources say Vice President Mike Pence has become a bit of a sounding board for Tillerson, and the two men often have lunch together. After the "moron" remark, an aide says Pence advised Tillerson on "setting expectations" and counseled him on how to work with the administration toward the President's goals.

"At no time did he and the secretary ever discuss the prospect of the secretary's resignation from the administration. Any reporting to the contrary is categorically false," said Jarrod Agen, Pence's spokesman.

A senior White House adviser said there is "certainly some friction there to say the least" between Tillerson and the White House but pointed fingers at West Wing staff rather than directly at the President. This person said Tillerson is "obviously growing frustrated because of the unpredictable nature of his job."

'They're all good'

Heather Nauert, the State Department spokeswoman, said that Tillerson and Trump spoke after the secretary of state's remarks on Wednesday.

"It was a good conversation and they're all good," she said. Nauert also said Tillerson told her he'd never used "moron" to describe the President.

But Trump isn't the only person in the West Wing who Tillerson has been at odds with. He became so "irate" with national security adviser H.R. McMaster earlier this year on a conference call that Defense Secretary James Mattis had to step in, an administration official directly familiar with the incident says.

"Tillerson and McMaster do not do well together," said the official, who left the administration several weeks ago in an unrelated matter.

This person, who is directly familiar with other multiple interactions involving Tillerson, declined to be identified because of the sensitivity of the matter.

During that conference call, Tillerson, Mattis and McMaster were discussing the way ahead on the proposed strategy for fighting the war in Afghanistan. McMaster was pressing for a faster decision-making process from the Pentagon and State Department. As the official described it, Tillerson finally became so irritated with the White House pressure, he said they could move ahead without him. It is not clear if that was a threat to resign.

"Voices were raised" during that call, the official said. Mattis then stepped in and reminded McMaster that the State Department and Pentagon did not have a significant number of Senate-confirmed senior staff officials who could quickly work these problems. The official said McMaster then realized "he overstepped" and backed off.

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But the official also describes a series of meetings and interactions in which Tillerson has become repeatedly irritated. The official said Mattis has tried to "mentor" Tillerson and treates him "with the respect of a peer, with talent, but maybe a guy without the political skills."

The official described private meetings in which Tillerson has become "a little more hotheaded" than he appears in public, using salty language, a trait that Mattis shares.

Though Tillerson's departure seems imminent, the friction between the President and his top diplomat may not have reached its boiling point yet. A person close to Tillerson said it has always been his plan to stay on at the State Department through the first year of the Trump administration but acknowledged again Wednesday that his future is "up to the President."

Trump recently seemed to undercut Tillerson when he said he was wasting his time attempting new dialogue with North Korea.

"I told Rex Tillerson, our wonderful secretary of state, that he is wasting his time trying to negotiate with Little Rocket Man," Trump wrote on Twitter. "Save your energy Rex. we'll do what has to be done!"

Despite this, White House press secretary Sarah Sanders said Monday that Trump still had confidence in Tillerson, despite their different messages on North Korea.